Browsing by Author "De Villiers, M S"

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    The effects of human disturbance on the seabirds and seals at sub-Antarctic Marion Island
    (2009) Wheeler, Mariette; De Villiers, M S; Underhill, Leslie G
    Animals at Marion Island can be affected by logistic disturbance (especially helicopter noise), incidental pedestrian disturbance and research disturbance. The responses of wandering albatrosses (Diomedea exulans) and king penguins (Aptenodytes patagonicus) were investigated through standardised pedestrian approaches. Intensity of behavioural responses and levels of prolactin (females only) indicated that adult wandering albatrosses had become sensitised by high levels of chronic disturbance. Responses were greatest during the Prospecting and Early Incubation phases. Frequency of disturbance did not influence behavioural responses, but birds visited most often over three consecutive days had the lowest chick survival. Guarding king penguins were less likely to move away during disturbance than non-breeding groups. Visit duration and approach distance affected behavioural responses. There was evidence of habituation by king penguins to current levels of incidental disturbance. Grey-headed albatross (Thalassarche chrysostoma) adults and chicks showed short-term behavioural responses to research disturbance, and recovery times were variable. Level of chronic disturbance did not explain breeding success differences between colony sections. Instantaneous scans or counts of guarding and brooding gentoo penguins (Pygoscelis papua), incubating Crozet shags (Phalacrocoraxmelanogenis), pre-fledging grey-headed albatross chicks and non-breeding king penguins were made before and during helicopter operations.
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    Populations of surface-nesting seabirds at Marion Island, 1994/5-2002/3
    (2003) Crawford, R J M; Cooper, J; Dyer, B M; Greyling, M D; Klages, N T W; Ryan, P G; Petersen, S L; Underhill, L G; Upfold, L; Wilkinson, W; De Villiers, M S; Du Plessis, S; Du Toit, M; Leshoro, T M; Makhado, A B; Mason, M S; Merkle, D; Tshingana, D; Ward, V L; Whittington, P A
    During the 1990s and early 2000s, populations of surface-nesting seabirds at Marion Island showed different trends, but for the majority of species numbers decreased. Reduced numbers of gentoo penguins Pygoscelis papua, eastern rockhopper penguins Eudyptes chrysocome filholi, Crozet shags Phalacrocorax [atriceps] melanogenis and probably macaroni penguins E. chrysolophus are most plausibly attributed to an altered availability of food. Decreases in numbers of dark-mantled sooty albatrosses Phoebetria fusca, light-mantled sooty albatrosses P. palpebrata, southern giant petrels Macronectes giganteus and possibly northern giant petrels M. halli may have resulted from mortality of birds in longline fisheries. However, populations of wandering Diomedea exulans and grey-headed Thalassarche chrysostoma albatrosses fluctuated around a stable level. Numbers of Subantarctic skuas Catharacta antarctica and kelp gulls Larus dominicanus breeding at Marion Island also decreased. Kerguelen Sterna virgata and Antarctic S. vittata terns remain scarce at the island. Trends for king penguins Aptenodytes patagonicus were not reliably gauged, but numbers probably remained stable or increased. There were large fluctuations in numbers of king penguin chicks surviving to the end of winter.